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Tissue Trimethyllysine Biosynthesis and Carnitine Content in Pregnant and Lactating Rats Fed a Lysine-Limiting Diet^1,2,

Departments of Surgery, Michigan State University and Butterworth Hospital, Grand Rapids, MI 49503

Previous studies have indicated that carnitine biosynthesis is primarily regulated by the availability of trimethyllysine. The present study investigated the rate of trimethyllysine biosynthesis during pregnancy in rats fed a lysine-restricted diet. Pregnant Sprague-Dawley rats were fed ad libitum a crystalline amino acid diet (18% amino acids) containing either 1.44% or 0.36% lysine. Food intakes were not significantly different between the two groups, either during 19 d of gestation or 12 d of lactation (p > 0.05). Trimethyllysine content and synthetic rates were not significantly different between the treatment groups for any of the five tissues tested at either of the two time points. Tissue carnitine content was not consistently affected by dietary lysine content. Liver carnitine content was significantly higher in control rat pups at 12 d of lactation than in pups in the lysine-deficient group. Pups in both groups had peptide-linked trimethyllysine levels in skeletal muscle that were 46% of those seen in the control adults. However, previous reports of higher protein turnover in the neonate would indicate that trimethyllysine is not limiting at this age. Under these experimental conditions, carnitine biosynthesis is not impaired because of restricted availability of trimethyllysine.

KEY WORDS: • carnitine • trimethyllysine • lysine • pregnancy • rats

¹ An abstract of this work was presented at the 73rd annual meeting of the Federation of American Societies for Experimental Biology, March 19–23, New Orleans, LA [DAVIS, A. T. (1989) Trimethyllysine biosynthesis in the pregnant rat fed a lysine restricted diet. FASEB J. 3: A940 (abs.)].

² Supported by Public Health Service grant 5R23HD20167-02, awarded by the National Institute of Child Health and Human Development.

³ Address requests for reprints to Dr. Davis at the Nutrition Research Laboratory, Butterworth Hospital, 100 Michigan, NE, Grand Rapids MI 49503.

Manuscript received 1 August 1989. Revision accepted 19 March 1990.